Electrical resistivity of U1−xMxBe13 under pressure

UC Irvine UC Irvine Previously Published Works Title ELECTRICAL-RESISTIVITY OF U1-XMXBE13 UNDER PRESSURE Permalink https://escholarship.org/uc/item/2wj8q05h Journal JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 76-7 ISSN 0304-8853 Authors BORGES, HA THOMPSON, JD ARONSON, MC et al. Publication Date 1988-12-01 DOI 10.1016/0304-8853(88)90378-2 License https://creativecommons.org/licenses/by/4.0/ 4.0 Peer reviewed eScholarship.org Powered by the California Digital Library University of California Journal of Magnetism and Magnetic Materials 76 & 77 (1988) 235-237 North-Holland, Amsterdam 235 ELECTRICAL RESISTIVITY OF U t_ xMxBet3 U N D E R P R E S S U R E H.A. BORGES, J.D. T H O M P S O N , M.C. A R O N S O N , J.L. S M I T H and Z. FISK Los Alamos National Laboratory, Los Alamos, N M 87545, USA Measurements of the electrical resistivity of Ul_xTh:,Be13 compounds as a function of pressure provide a possible explanation for the unusual behavior of these materials. and the latter is argued for from pressure measurements [5] of T~ vs. x. Previously we have shown [6] that pressure modifies the temperature dependence of the resistivity to of pure UBe13, particularly at low temperatures where p reaches a m a x i m u m at T = Tma~ -2.5 K. Further, there appears to be an inverse correlation [7] between Tm~ and the pressure dependent electronic specific heat y(P), i.e. ~,(P) (x I / T m ~ ( P ). Ambient pressure specific heat and resistivity measurements on UBe~3 and U~_xTh x Bet3 also show that y ( T ~ 0) depends sensitively Thorium substitution into Ua_xThxBe~3 affects both the superconducting and normal state properties [1]. Particularly interesting is the appearance of a cusp in the superconducting transition temperature T~ at x =0.0172 and a second phase transition a t Tc2, below T~, for 0.019 < x < 0.04 [2]. Muon spin rotation experiments [3] detect a magnetic moment of - 1 0 - 3 / ~ B / U for T < T~z, suggesting that this transition is magnetic or that it is associated with an exotic superconducting phase that has a magnetic moment. The former interpretation is supported by ultrasonic data [4] 1O0 [ 1 ~ . U9,828 ho172Be13 ,\ 2.1 .-..E - 1.9 Ill O U9828Th°172Be13 ~ " -, ,.,,, ~'",, N, \ .. \ \ . ,, " . . . \, 1.5 ~ ~ °:,-.. : ; - 4 ~ "A. "-, • °°°°° 08o 0 J 5 I 10 i .. " ' ' ' - - O 1.0 • 6.2 • 9.6 • 12.7 1.3 ........ ,, "~'I o 62 kbar • 96kbar I 5 ~' I ,o J L ~s i T'q-m~ bar kbar kbar kbar , • • L 15 16.3 kbar 18.4 kbar , I 20 , 25 TEMPERATURE (K) Fig. 1. Electrical resistance R of Uo.9828Tho.o172Be13 at various pressures as a function of temperature T. The inset shows the same data but now the resistance has been normalized by its maximum value R max and the temperature by the value at which R max Occurs. 0304-8853/88/$03.50 © Elsevier Science Publishers B.V. 236 H.A. Borges et al, / Electrical resistivity of U1 ~ M~ Be 1~ under pressure on the unit cell volume [8] with ,/ increasing and Tm~~ decreasing as the volume increases, which is the case with Th substitution. Here we report pressure studies on the resistivity of U~ ffh~Be~3 for x = 0, 0.0093, 0.0172, 0.0340 and 0.0536. Details of the sample preparation and procedure for resistivity measurements under modest hydrostatic pressures have been described earlier and will not be reiterated here. As an example of our results, we show in fig. 1 the effect of pressure on the resistance R of U0.gs28Th0.0172 Be13, the composition where the cusp in T~(x) appears. At ambient pressure, there is no peak in p for T>~1.2 K, but for P>~6.2 kbar, T ~ x appears at low temperatures and is observed to move to higher temperatures with pressure. As is true for UBe~3 [6], we find that the curves of fig. 1 can be scaled onto each other by normalizing R b y Rmax(Rma x = R ( r m a x ) ) and T by T.,~x (fig. 1 inset) and further that the scaled curves for both x = 0 and 0.0172 compare favorably. This suggests that R m~x has the same physical origin in both samples. For x = 0.0340 and 0.0536, no peak in p ( T ) was found above 1.2 K up to the highest pressures studied, 14.9 and 17.2 kbar respectively. However, qualitatively we can scale all data for 0 ~< x ~ 0.0536 onto each other by assuming that 1 a / o Th produces a negative chemical pressure of 7 kbar, a value much larger than expected ( 0.45 k b a r / a / o ) on the basis of lattice parameter changes [1] alone. This implies that Th substitution does more than simply expand the lattice. Fig. 2 compares the pressure dependence of Tmax for UBeI3 to that of U~_~ThxBe13 with x = 0.0093 and 0.0172. In the case of UBe13, dTmax/d P is linear from P = 0; however, in the Th-doped samples there appears to be two regions of differing dTm~x/dP. For x = 0.0093, the change in slope occurs for P ~ 6 kbar; whereas, for x = 0.0172 the slope change takes place near 16 kbar. The highpressure slopes of both are close to that of UBe~3. Further, the pressure at which the slope change occurs is approximately that pressure required to compensate the negative chemical pressure produced by Th substitution. Pressure measurements of T for x = 0.019 and 0.026 reveal a "kink" in T~( P ) at the temperaturepressure points (0.48 K, 1.3 kbar) and (0.20 K, 5.2 kbar) respectively [5]. From an extrapolation of our Tm,x ( P ) vs. x data, we can estimate the - 6 • 0 I - ,Th r . . . . Be I , 3 I~ ,kbar 2 +,.~,,kba 1i 0~ 0 r ..... ~" / / " ~ 0 15 K, kbdr / • UNDOPED : 0 932o~TTh ~ a 4 8 --' 12 i6 " 20 PRESSURE (kbar) Fig. 2. T e m p e r a t u r e at which the resistance m a x i m u m appears T,,,a ~ as a function of pressure for U I , T h , B e l ~ with x - 0. 0.0093 a n d 0.0172. temperature at which Tm~x should appear for (x, P) corresponding to those producing the kink in Tc(P). Within the estimated uncertainty in both experiments, Tm,x(X, P) is coincident with the kink in T~(x, P), suggesting that with pressure the kink arises from the passage of Tm~~ from below T~ through the T (x, P) phase boundary. That Tmax be below Tc appears to be a necessary condition for the development of the second phase transition. However, Tm~x clearly is not equivalent to T~2 because dTm~x/dP>O but dT~2/dP < 0 [9]. The variation of o(T) and the increase of ~ , ( T ~ 0) at ambient pressure with x suggest that the single-site Kondo temperature T K is a decreasing function of x, thereby enabling magnetic interactions to become more significant. A possible explanation for the second phase transition is that it originates from magnetic interactions made possible by the lowered T K with Th substitution. Applied pressure would raise T K relatively rapidly, producing dT~n~x/dP> 0 but also suppressing magnetic correlations responsible for the second phase transition, i.e. dT~2/dP < 0. This simple picture also would predict that B substitution for Be could produce a second transition below T~, as appears to be the case [10]. Certainly, this interesting system requires much further study before it is well-understood. Work at Los Alamos was performed under the auspices of the US DOE. H.A. Borges et al. / Electrical resistivity o f U1 _ x M x B e 1 3 under pressure References [1] J.L. Smith, Z. Fisk, J.O. Willis, A.L. Giorgi, R.B. Roof, H.R. Ott, H. Rudigier and E. Felder, Physica B 135 (1985) 3. [2] H.R. Ott, H. Rudigier, Z. Fisk and J.L. Smith, Phys. Rev. B 31 (1985) 1651. [3] R.H. Heffner, D.W. Cooke and D.E. MacLaughlin, in: Theoretical and Experimental Aspects of Valence Fluctuations and Heavy Fermions, eds. L.C. Gupta and S.K. Malik (Plenum, New York, 1987) p. 319. [4] B. Batlogg, D. Bishop, B. Golding, C.M. Varma, Z. Fisk, J.L. Smith, and H.R. Ott, Phys. Rev. Lett. 55 (1985) 1319. [5] S.E. Lambert, Y. Dalichaouch, M.B. Maple, J.L. Smith and Z. Fisk, Phys. Rev. Lett. 57 (1986) 1619. 237 [6] J.D. Thompson, M.W. McElfresh, J.O. Willis, Z. Fisk, J.L. Smith and M.B. Maple, Phys. Rev. B 35 (1987) 48. [7] J.D. Thompson, H.A. Borges, Z. Fisk, S. Horn, R.D. Parks and G.L. Wells, in: ref. [3], p. 151. [8] H.R. Ott and Z. Fisk, in: Handbook on the Physics and Chemistry of the Actinides, eds. A.J. Freeman and G.H. Lander (North-Holland, Amsterdam, 1987) p. 85. [9] R.A. Fisher, S.E. Lacy, C. 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